Bag machines for making bags from thermoplastic web material can be arranged to make side weld or bottom weld bags. Side weld bags are made by unwinding a roll of thermoplastic material and folding it along or adjacent its longitudinal median. The folded web is fed stepwise over an intermittently rotating platen roll providing support for a transverse band of the web. Over the platen roll, a transversely extending reciprocably mounted seal bar is provided that engages the web effecting sealing and severance thereof when it comes into pressure engagement with the platen roll. As the seal bar is moved vertically upwardly, the platen roll is immediately rotated at a surface speed greater than the initial speed of the web in order to overcome the tendency of the web, which has been rendered molten while it is in contact with the platen roll, to stick to the platen roll. As will be pointed out hereinafter, bag machines set up to produce bottom weld bags exhibit the same tendency but until the advent of the present invention no satisfactory means were available to reliably insure stripping of the web to prevent adhesion with the seal bars.
Bottom weld bags are made by supplying the thermoplastic film in tubular form, whether it be gusseted or non-gusseted. Some machinery is provided with sealing and cutting bars operating to transversely cut and seal the web at longitudinally spaced intervals so that the mouth of the bag is the portion which is initially fed to stacker belts, which are designed to transport the completed bag to a stacking table. The disadvantages of having the mouth of the bag leading into the stacker belts has been recognized and its main deficiency is that the bag has a tendency to inflate due to the rapid movement of the film from the seal bar area to the stacker belts. Some machines which are presently available cut and seal the film so that the bag bottom is fed first into the stacker belts avoiding or completely eliminating the possibility of inflating the bag.
Bag machines, whether they are producing side weld or bottom weld bags, require for commercial acceptability the ability to stack bags in a neat pile wherein the margins of the bags are vertically aligned much like a deck of cards. Among the many elements that contribute to this result, bag pick-off accuracy and transportation of the individual bags by the stacking conveyor are major factors. As will be pointed out hereinafter, the subject matter of the invention provides an apparatus and method that will reliably and consistently transport and stack bags in a registered pile.
Production of bottom weld bags necessitates transverse cutting of the web adjacent the bottom seal. It is usual practice to cut the web from one-eighth to five-sixteenths of an inch from the weld producing, what is commonly known in the industry, a skirt. To perform the cutting, known prior art devices comprise a series of thin knives such as razor blades mounted on a rigid bar to define a saw-tooth configuration. Problems with this arrangement continually arise occasioned by bending of the knives resulting in uncut portions of the web which effect the orientation of the bag as it is received and transported by the stacker belts. The invention provides a remedy for this condition as the means employed for transversely cutting the web include a continuous rigid cutting blade not subjected to deformation or bending.